The FBI has searched former President Donald Trump's Mar-a-Lago estate as part of an investigation into whether he took classified records from the White House to his Florida residence.

Trump disclosed the action in a lengthy statement, asserting that agents had broken into his safe in a search he decried as evidence of “dark times for our nation".

The action, which the FBI and Justice Department did not immediately confirm, marks a dramatic escalation in law enforcement scrutiny of Trump and comes as he has been laying the groundwork to make another bid for president. 

Donald Trump's Mar-a-Lago estate. – AP

“After working and cooperating with the relevant Government agencies, this unannounced raid on my home was not necessary or appropriate,” Trump said in his statement.

He added: "These are dark times for our Nation, as my beautiful home, Mar-A-Lago in Palm Beach, Florida, is currently under siege, raided, and occupied by a large group of FBI agents. Nothing like this has ever happened to a President of the United States before.”

Justice Department spokesperson Dena Iverson declined to comment on the search, including about whether Attorney General Merrick Garland had personally authorised the search.

The Justice Department has been investigating the alleged presence of classified records inside 15 boxes that were retrieved from Mar-a-Lago by the National Archives and Records Administration earlier this year. The Archives then referred the matter to the Justice Department.

The Archives in February notified Congress that it had recovered about 15 boxes of White House documents from Trump's Florida home, some of which allegedly contained classified materials.

Police direct traffic outside an entrance to former President Donald Trump's Mar-a-Lago estate. – AP

The US House of Representatives Oversight Committee at that time announced it was expanding an investigation into Trump's actions and asked the Archives to turn over additional information.

Trump previously confirmed that he had agreed to return certain records to the Archives, calling it "an ordinary and routine process".

Federal law bars the removal of classified documents to unauthorised locations, though it is possible that Trump could try to argue that, as president, he was the ultimate declassification authority.

Trump and his allies immediately sought to cast the search as part of a Democratic-driven effort to keep him from winning another term in 2024, even though the Biden White House said it had no prior knowledge of it and the current FBI director, Christopher Wray, was appointed by Trump five years ago and served as a high-ranking official in a Republican-led Justice Department.

In his first public remarks since news of the search surfaced, Trump made no mention of it during a tele-town hall on behalf of Leora Levy, the Connecticut Republican he has endorsed in US Senate primary to pick a general election opponent against Democratic US Senator Richard Blumenthal.

The probe is not the only legal headache confronting Trump. A separate investigation related to efforts by Trump and his allies to undo the results of the 2020 presidential election and the January 6, 2021, riot at the US Capitol has also been intensifying in Washington.

And, a district attorney in Fulton County, Georgia, is also investigating whether Trump and his close associates sought to interfere in that state's election, which was won by Democrat Joe Biden.